The present invention is directed to a process for extracting lipids from microorganisms without the use of any significant amount of an organic solvent.
A typical microorganism lipid manufacturing process, such as production of omega-3 highly unsaturated fatty acid, in particular docosahexaenoic acid (DHA), involves growing microorganisms which are capable of producing the desired lipid in a fermentor, pond or bioreactor, isolating the microbial biomass, drying it, and extracting intracellular lipids with an organic solvent, e.g., hexane. Generally, intracellular lipids of microorganisms are extracted after rupturing (i.e., lysing) the cells of the microorganisms. The extracted lipids are can be further refined to produce a high purity and/or quality lipids. The microorganisms are generally isolated by first diluting the fermentation broth with water, and centrifuging the mixture to isolate microorganisms. When lipids are not extracted immediately or soon after isolating the microorganisms, the isolated microorganisms are typically dried, for example, on a drum dryer, and packaged, for example, in vacuum-sealed bags, to prevent degradation of lipids.
Unfortunately, the drying process exposes the microorganisms to heat, which can damage, i.e., degrade the quality of, lipids if done incorrectly. The vacuum-sealed bags may develop leaks, which can further degrade the quality of the lipids due to exposure of the microorganisms to air. In addition, if the dried microorganisms are not treated with an antioxidant, lipids can be further degraded due to exposure to air, for example, DHA may degrade due to oxidation by air. Furthermore, in some cases operators who are exposed to the dried microorganisms can develop an allergic reaction creating a safety and/or health hazard to operators.
Moreover, in an industrial scale production, the amount of organic solvent used in lipid extraction typically requires a large amount of volatile and flammable organic solvent, thereby creating hazardous operating conditions. The use of organic solvent in the extraction process may necessitate using an explosion-proof oil recovery system, thereby adding to the cost of lipid recovery. Moreover, use of an organic solvent in extracting lipids from microorganisms generate an organic solvent waste stream requiring a proper method, which further increases the overall production cost of lipid extraction.
Therefore, there is a need for a process for extracting lipids from microorganisms which does not require the use of an organic solvent. There is also a need for a lipid extraction process from microorganisms which does not require the expensive step of drying the microorganisms.
The present invention provides a process for obtaining lipid from microorganisms comprising:
(a) lysing cells of the microorganisms to produce a lysed cell mixture;
(b) treating the lysed cell mixture to produce a phase separated mixture comprising a heavy layer and a light layer;
(c) separating the heavy layer from the light layer; and
(d) obtaining the lipid from the light layer.
The lysed cell mixture may contain an emulsion, in which case the emulsion can be separated by centrifuging the lysed cell mixture. The separated lysed cell mixture comprises a heavy layer which contains aqueous solution and a light layer which contains lipids, which may be emulsified. The aqueous solution comprises solid cell materials which results from lysing cells. The light layer can be further washed with an aqueous washing solution until the lipid becomes substantially non-emulsified.
When the lipid extraction process of the present invention includes using microorganisms from a fermentation process, the extraction process can also include solubilizing at least part of proteinaceous compounds in a fermentation broth, by adding a base selected from the group consisting of hydroxides, carbonates, bicarbonates and mixtures thereof.
The process of the present invention can also include heating the microorganisms to temperature of at least about 50xc2x0 C.
Preferably, the microorganisms are capable of growth at salinity level of less than about 12 g/L of sodium chloride, more preferably less than about 5 g/L of sodium chloride and most preferably less than about 3 g/L of sodium chloride.
Preferably, the microorganisms comprise at least about 30% by weight of lipid, more preferably at least about 35% by weight, and most preferably at least about 40%. Alternatively at least about 30% of the lipid is docosahexaenoic acid, preferably at least about 35%, and more preferably at least about 40%.
In one particular aspect of the present invention the microorganisms are capable of producing at least about 0.1 grams per liter per hour of docosahexaenoic acid, more preferably at least about 0.2 g/L/h, still more preferably at least about 0.3 g/L/h, and most preferably at least about 0.4 g/L/h.
In another aspect of the present invention, the microorganism is selected from the group consisting of algae, fungi, bacteria and protist. Preferably, the microorganisms are of the order Thraustochytriales. More preferably the microorganisms are selected from the genus Thraustochytrium, Schizochytrium and mixtures thereof. And most preferably, the microorganisms are selected from the group consisting of microorganisms having the identifying characteristics of ATCC number 20888, ATCC number 20889, ATCC number 20890, ATCC number 20891 and ATCC number 20892, mutant strains derived from any of the foregoing, and mixtures thereof.